In general, a diesel engine is provided with a supercharger or an intercooler in order to obtain a higher output.
In the diesel engine having the supercharger as described above, exhaust gas or outside air is compressed by a compressor of the supercharger, and the compressed exhaust gas or the compressed air is supplied to the engine.
However, the rapidly compressed air absorbs heat of the supercharger and heat generated during the process of compressing the air, such that density of the air decreases. As a result, charging efficiency in a cylinder of the engine deteriorates.
For this reason, the intercooler is used to cool the air, that is, supercharged air, to increase air density and to allow a larger amount of air to be drawn into the cylinder of the engine. Accordingly, it is possible to obtain higher output.
Furthermore, an exhaust gas recirculation (EGR) system is mounted in the diesel engine in order to reduce emission of nitrogen oxide (NOx) that is one of air pollutants.
The nitrogen oxide is deleterious gas generated when oxygen and nitrogen are combined under a high-pressure and high-temperature condition. In order to inhibit the generation of the nitrogen oxide, the EGR system lowers a combustion temperature by supplying an intake system with a part of exhaust gas discharged into the atmosphere and reduces the generation of the nitrogen oxide by reducing the amount of oxygen to be supplied.
The EGR system needs to recirculate high-temperature exhaust gas, and as a result, the EGR system may be provided with an EGR cooler to cool the EGR system. As the EGR cooler, there are a high-pressure EGR cooler (HP-EGR cooler) which is connected to an EGR valve at a side of an exhaust manifold and directly cools high-pressure EGR gas flowing to the intake manifold, and a low-pressure EGR cooler (LP-EGR cooler) which cools low-pressure EGR gas with a pressure lowered while the gas sequentially passes through a turbine of the supercharger, a catalyst converter and the like.
Recently, a water-cooled intercooler, which makes an intake route short, is applied to the engine system in order to improve cooling efficiency and responsiveness. In particular, researches have been conducted to simplify a complicated cooling circuit connected to the intercooler and the EGR cooler, make the entire structure compact, and improve intake efficiency by preventing gas passing through the intercooler and the EGR cooler from being heated before the gas is supplied to a combustion chamber.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.